Yamaha RX-797 going into protection

[Francesc V.]

Hi:

I am trying to rescue this Yamaha amplifier. It turns on, does some relé clics and then switwes off.

Following up the service manual, I've entered into diagnosis mode (Fm + 8 + switch on during 3 secs to avoid protection). It shows the error shown in one of the pictures. If I am not misunderstood it might be a power supply issue.

These are the voltages I am getting in CB272 connector (page 33)

Amplifier just plugged in:

S10 -> 9.7-10.3V (quite unstable voltage)
PRY -> -122mV
E -> -108mV
PDET -> 5.06V
+5M -> 5.10V
/RES -> 4.99V

As soon as I switch on........voltages decreases dramatically (3 rele clicks and let's start again).

S10 -> 8.85V
PDET -> 4.02V
+5M -> 4.03V
/RES -> 3.76V

I've checked the 2 boards that make the power supply unit. All seems to be correct at component level......but I guess it's obvious that might be not true, right? or there is something outside that drains so much current? (I don't think so as the voltages in standby mode "dance" quite a lot.


Any guidance is more than welcome.

[budwich]

Re: Yamaha RX-797 going into protection

start by checking the voltages shown on page 30 for the power supply area.

[Francesc V.]

Re: Yamaha RX-797 going into protection

Thank you so much for the hint, budwich. Indeed the picture help me to realise that more likely is the transformer that has gone. I mean.......it's not normal the the primary has 3.5K impedance, right???


Other topic is that this transformer including shipment will cost about 30€!!! (I saw it in ebay). Any alternative you might consider?

Is it a 115VAC - 12.8V right?

Regards,
Francesc.

[lotas]

Re: Yamaha RX-797 going into protection

This is a low power transformer, so 3.5 kOhm is fine, as long as there is no open circuit.

[budwich]

Re: Yamaha RX-797 going into protection

As suggested, I would do some voltage checks first. You should be able to readily find the power in points and outs for the transformer among other things. I would think its more likely a lost rectifier or possibly a cap depending on what you find.

[Francesc V.]

Re: Yamaha RX-797 going into protection

Hi:

I've started with voltage measurements following the schematics on page 30, but everything "seems" ok.



Also power supply unit seems ok:

S10 -> 9.9 stable
PRY -> -122mV
E -> 0V
PDET -> 5.06V
+5M -> 5.10V
/RES -> 4.99V

When I enter into the "protected menu" and check menu 3 (AD DATA check) I got different numbers based whether I click or not (cd direct amp / pure direct).........not sure if they are telling you something.

Any suggestion / next step more than welcome.

Regards,
Francesc.

[budwich]

Re: Yamaha RX-797 going into protection

I guess my question would be when did you measure / monitor the points.... just after startup, as many as quick as possible before shut down, monitored each until shutdown?

Just guessing based on your initial display of the "B" in the protection display that the "B" supply has an issue.... certainly just a guess. what is sw101? what is set to?

[Francesc V.]

Re: Yamaha RX-797 going into protection

Measurements were done just after the startup (I had about 2 secs before turning off). However once measured, I realised that keeping the unit in protection mode, I got the same measurements (they started a little bit low, but then voltage increased).

What is the "B" that is shown in the display? is it refering to the "main 2"? No idea what the amp. is trying to tell me. If anybody does, please shout.

SW101 is the speaker selector. It's set up to -> 6ohm(a or b) / 12ohm (a+b)

[budwich]

Re: Yamaha RX-797 going into protection

sorry I don't know what "B" means but was guessing it is referring to the "B" voltage. On some other receivers, I have seen something like that refer to the different power boards.
In terms of the switch, have you tried switching it to the other position which is what?... and again taking measurements.

Further, since you have seen that the basic power outputs appear to be good, then it would appear the problem is further along in the DC domain somewhere.

Looking at the SM again... the "B" doesn't appear to have much meaning as it is some sort of "version" letter (very poor explaining by yamaha... but I guess if one is a yamaha tech, then it would be obvious... :-) ).

[budwich]

Re: Yamaha RX-797 going into protection

In the protect menu, what is the history reporting?

[budwich]

Re: Yamaha RX-797 going into protection

Hi:

I've started with voltage measurements following the schematics on page 30, but everything "seems" ok.



Also power supply unit seems ok:

S10 -> 9.9 stable
PRY -> -122mV
E -> 0V
PDET -> 5.06V
+5M -> 5.10V
/RES -> 4.99V

When I enter into the "protected menu" and check menu 3 (AD DATA check) I got different numbers based whether I click or not (cd direct amp / pure direct).........not sure if they are telling you something.

Any suggestion / next step more than welcome.

Regards,
Francesc.

I think you were on the right track with checking the 5v area. But I see this is a bit different from your first post which indicated that the +5M value dropped when "on" was pressed.... why?

Also what is the "5BU" value?

[Francesc V.]

Re: Yamaha RX-797 going into protection

Don't be sorry.......thanks for the support. :-)

I don't discard anything........it could be the power supply, it could be the DC circuit.

Regarding the DC circuit, I've just measured the 8 big transistors, and nothing seems weird.

- Collectors: 54V / -54V
- Bases: 0.6V / -0.6.V
- Emitters: 10mV / -10mV

Keep on analysing......

[budwich]

Re: Yamaha RX-797 going into protection

The error points towards the power supply as opposed a "dc level" where it shouldn't be on the amp end of things. I think your first post of values in the 5v power area needs to be re-visited / clarified. IC601 regulation seems to be "off" if your early numbers reflect what is around there.

[budwich]

Re: Yamaha RX-797 going into protection

more questions: does your unit have an "XM module". Your notes appear to "X" that out.
When I track thru the SM, there are TWO items which seem "interesting". You seem to have tracked on PRY while I have tracked PRV. I am thinking there might be a "typo" in the system although I have track thru the whole thing BUT PRV tracks back from the XM module and goes to the ps protection pin on the main processor, pin 90. I see now that the PRY i s going to the power relay pin on the same processor chip.

Of course, take my comments with some salt as I have limited experience with yamahas (although I have two both have forms of hdmi board problems and more)... so I am learning to flow thru the schematics a bit better but not sure that means much. :-)

You should monitor pin1 cb24 ... shown on page 34. Based on the circuit, it should be some value less than 5 going towards the processor.

[Francesc V.]

Re: Yamaha RX-797 going into protection

- Unit does not have the XM module. I just wrote "not exist" on the sheet. :-)
- IC601 does give the 5.3V..........also the next 3 diodes.
- Pin13 in IC602 does fluctuate.

I will need a little bit of lack on this one. Thanks for your feedback.

[budwich]

Re: Yamaha RX-797 going into protection

Your "lack" (luck :-) ) ... our luck is always needed on these things.

I hope that you had a typo error with IC602 pin 13... not sure what you mean by that... if that is the right pin, I would expect it to oscillate as it is an oscillator output... is the output correct as shown in page 22... not sure what it has to do with things... I guess perhaps it is feed else where in the circuit which might be an issue if it isn't "nice".

[budwich]

Re: Yamaha RX-797 going into protection

Another question... what is the history of the unit... how did it get to this state? Have you tried reloading the firmware? I am still tracking thru the schematics to find out what's up with the PRV line

ADDED: found another PRV line. Page 31... its coming from the "func 3" area CB451. That one doesn't appear to have a direct link to 5v but to "LB". Hope this is the right "track".

ADDED some more... :-) I now see lots of PRV in various areas ... :-( Luck or lots of working tracing / checking each path.
one of the voltages that looks interesting is the +LB on page 33

[Francesc V.]

Re: Yamaha RX-797 going into protection

Finally it's working!!!

I bought it as faulty for 20€. It was in protection mode......turning on and then turning off.

First thing I did was to focus on the power supply....initially it had unstable voltage......but I manage to fix it.

The main problem was that I was testing the unit without any additional card, just the main PCB, and then protection was acting. I know it now.

Second problem was also that PCBs were not screwed, so there wasn't a good earth.

So basically, once I haven't found any issue, I assembled and it started working.

[budwich]

Re: Yamaha RX-797 going into protection

great... good work. Glad it worked out. I learned some stuff from going thru the schematics that I hope to "transfer" to my issues with some yamahas that I have. They operated but some times they shut down for no reason and some times they do go into PS1 prt mode... so something is "marginal". Enjoy your "new" receiver.